Hydraulic power element



July 15, 1958 F. A. GREENAWALT HYDRAULIC POWER ELEMENT Filed March 27.1953 COPOLYMEB OF BUTAD/ENE AND ACRVLONITR/LE 98% I SOBU TAA 2% ISOPRENEl8 l3 l0 INVENTOR. FfifUfE/CK A. fieawmmq United States Patent 2,843,151riYnRAULic POWER ELEMENT Frederick A.- Greenawalt, Columbus, Ohio,assignor to Rfalbco' Incorporated, Columbus, Ohio, a corporation 0 hio 7Application March 27, 1953, Serial No. 345,065

3 Claims. (Cl. 137 -788) The present invention relates to power elementsfor actuating control mechanisms 'orthe like, and more particularly to anew and improved expansible power element for providing a relativelylengthy power stroke in response to relatively small changes in volumeof a fluid, such as a body of confinedthermally expansible liquid.

An object of the invention is the provision of an improved pressureoperated power element comprising elastic, rubber-like material in theform of ian open ended tube having a transverse wall intermediate theends thereof forming a resilient or elastic liquid impervious partion inthe tube, a relatively rigid sleeve containing the tube to preventradial expansion thereof, annularly arranged abutment means associatedwith the sleeve and against which one end'of the tube abuts to preventlongitudinal movement of the tube in one direction, and a fluidinletstructure associated with the sleeve at the other end of thetube-and with which the tubeis sealingly secured so that fluidintroduced into the inlet structure causes the transverse wall to'movewith changes in volume of the fluidinside'the tube, the abutment meanspreventing longitudinal movement of the tube proper by the force of thefluid whereby the transverse wall moves longitudinally of the sleeve byflexing and internal flow of the resilient mater'ial in response togiven changes in the volume of the 'fluid, whichrnovementmay' beimparted to a plunger or the like engaging the outer face of the wall. v

Although the elastic tubular element may beof a' single piece, in thepreferred form of the invention described herein it comprises tworesilient cup-shaped members having somewhat different physicalcharacteristics and arranged'withthe bottom or end walls abutting oneanother to form the transverse wall and the open ends facing in oppositedirections, one member being'formed of elastic material relativelyimpervious to the passage of liquidtherethrough or the absorption ofliquids therein, and which is secured in'liquid sealing relationshipwith the fluid inlet structure, and the othermember being formed of'mate'rialhavingrelatively quick recovery from deformations thereofandresistant to'abrasion and adapted to receive :acontrol mechanismactuating plunger or the like therein.

The invention makes possible the utilization of rubher-like material toprovide an expansible element having substantially uniform powermovements to actuate control mechanisms, suchas switches or valves, inresponse to predetermined changes in volume of. a thermally expansibleliquid contained in the element and which operates under'fluid pressuresof one thousand pounds per square inch and higher whereby controldeviceactuating movements may be obtained in response to changes in-volume ofa relatively small quantity of liquid, thus permitting relativelysensitive responses to changes in temperatures, for example. The formand arrangement'ofthe components of the improved power element are suchthat there is no appreciable wear on the moving parts, particularly therubber like parts, so that 2,843,151 Fatented July 15, 1953 ice 2 thepower element is long lasting and accurate in operation'. 7

Other objects-and advantages of the invention will be apparent from thefollowing description of preferred em bodiments of the invention,reference being made to the accompanying sheet of drawings wherein:

Fig; 1 is an elevational view of a power element embodying theinvention;

Figs. 2 and 3 are sectional views of the power element but on a largerscale than shown in Fig. 1, showing certain parts thereof in diflerentoperative positions; and

Fig. 4 is a sectional view of another form of exparisi ble unit whichmay be employed in the improved power element.

As mentioned previously, the improved power element isparticularlysuitable for use as a thermostat to actuate control devices,such as valves or switches, in response to changes in temperatures,although it may be employed for other uses, and it is here shown anddescribed embodied in-a thermostatic device T. The thermostat T includesa base 10, which may be suitably attached to the housing orframe of acontrol mechanism (not shown), a sleeve 11 and an actuating plunger 12.The upper end of the plunger 12, as viewed in the drawings, is adaptedto engage a movable control member of the control mechanism to which thethermostat is attached to provide power movements to actuate the controlmechanism.

The base 10 is' preferably of relatively rigid material, such as brass,in the form of a cup having a bottom wall 13 with a central upwardlyprojecting stem 15. A radially extending bore 16 is formed in the bottomwall which receives one end of a capillary tube 17 which is brazed orotherwise suitably secured to the walls of the bore to form a fluidtight connection therewith. An axial bore 18 extends from the inner endof the bore 16 upwardly through the stem 15 to provide a fluid conduitfrom the tube 17 to the interior of the base 10. The other end of thetube 17 is not shown, but it may be sealed in any suitable manner orconnected with a'bu'lb. In either event the-tube and bulb, if any,'arefilled with a suitable liquid which expands and contracts in response topredetermined increases and decreases in temperature, as is well knownin the'art.

-A cup-shaped member 20 is disposed in an inverted position over thestem 15 and is secured in liquid tight relation with the bottom wall ofthe base 10 by a flange 21 projecting radially from the open end thereofand clamped to the bottom of the base by the lower end of 'the sleeveII, which surrounds the member. The flange 21 has an upstanding bead orrim 22 and the lower end of the sleeve 11 is undercut to receive thehead. The sleeve is secured in pressing engagement with the flange 21 bythe upper edges of the member 10 rolled inwardly over an annularshoulder 24 formed about the sleeve 11, as shown. The member 20 isformed of a rubber material relatively impervious to liquids andparticularly to the liquid employed in the tube 17. Rubber as used inthis-specification and the claims includes natural and conventionalsynthetic rubbers. A suit-able material is known as Butyl and comprisesa copolymer of about 98% isobutylene and 2% isoprene.

A second cup-shaped resilient member 26 is disposed within the sleeve 11and its bottom wall 27 rests on the top or end wall 28 of the member 20.In assemblying the power element, the member 26 is inserted into thesleeve 11 before the sleeve is secured to the base 10, as described.Member 26 is preferably formed of elastic material resistant to abrasionand having the property of quickly returning to its original form afterextension or stretching thereof. One such material is a nitrile syn:thetic rubber known as Buna-N rubber and comprising a copolymer ofbutadiene and acrylonitrile. The two members 20, 26 disposed as shownform a tubular unit having a transverse wall formed by the contiguousend walls 27, 28 of the members and which transverse walls form a fluidtight, elastic partition integral with the tubular walls of therespective members. The sides and end wall 28 form an expansible liquidtight chamber 29 in communication with the tube 17 through bores 18, 16.

In some instances, it might be desirable to eliminate the tube 17, bores16, 18 and confine, a body of liquid inside the chamber 29. In thatevent, the volume of the liquid in the chamber would vary according tothe temperature of the base 10. V If desired, the two members 20, 26could be replaced by a single elastic member, such as that shown at 30,having tubular side walls 31, a transverse wall 32 formed integral withthe tubular walls, and a radially extending flange 33 at one end similarto flange 21.

The sleeve 11 has an annular abutment or shoulder 37 formed about theinside thereof which engages the upper end edges of the member 26 whenthe sleeve is attached to the base 10, as described. The abutment 37prevents upward movement of the member 26 proper, as is discussed morefully hereinafter.

A cylindrical plug 40 is disposed in the recessed portion of member 26and is preferably formed of tetrafluoroethylene resin known as Teflonthe surface of which has a waxy or soap-like character insofar as itsfrictional property is concerned so that the friction between the plugand the insides of the member 26 is inconsequential to operation of thepower element. The lower end of the plunger 12 rests on the plug 40 andis adapted to slide freely in the sleeve 11. The upper end of theplunger, as viewed in the drawings, has a head 42 which rests on theupper end of the sleeve when the member 20 is in its normal orunexpanded condition as shown in Figs. 1 and 2.

The tube 17, bores 16, 18 and chamber 29 are filled with a suitableliquid mentioned previously, and in use the tube 17 or a major portionthereof is disposed in an area the temperature of which is to becontrolled, for example. As the temperature increases, the volume of theliquid increases and causes an increase in liquid volume inside thechamber 29 causing the end wall 28 of the member 20 to stretch and bulgeupwardly. The sides of the member 20 are prevented from radial expansionby the sleeve 11, and longitudinal movement thereof is prevented by theannular abutment 37 since the sides of the members 20, 26 aresubstantially non-compressible. As a result, the wall 28 bulges upwardlyand causes wall 27 of member 26 to be moved upwardly as illustrated inFig. 3. Since the material forming the sides of member 26 cannot moveupwardly along the inside of the sleeve 11 it flows inwardly andupwardly causing wall 27 to increase in thickness and thereby move theplug 40 upwardly, as is illustrated in Fig. 3. This action occurs byreason of the relatively high pressures available for action on theelastic members, and it is to be noted that by the arrangement shown,these high liquid pressures can be contained by the sealing structureformed between the flange 21 and the base and sleeve 11. The movement ofthe intermediate wall formed by the adjacent walls 27, 28 is such thatthere is no appreciable abrasion thereon and long life of consistentoperation is obtained. The member 20 retains the liquid and is actedupon by the member 26 to be returned to its normal position followingstretching of the wall thereof, and member 26 is resistant to 'abradingby the movement of plug 40 therein.

As mentioned previously, the movement of the plunger 12 may berelatively great with respect to the change in volume of the liquid inthe chamber 23 so that the power element may be quite sensitive tochanges in temperature and at the same time the power element may berelatively small and compact. For example, an element having theapproximate proportions shown in the drawings in which the outsidediameter of the members 20, 26 is approximately .250" and the diameterof chamber 23 about .120", will provide a power stroke of .070" andmore.

It will be seen that the improved power element may be madeinexpensively and provides accurate and long lasting operation. Whilebut two forms of the invention have been shown, it is to be understoodthat other forms, modifications and adaptations could be made all ofwhich fall within the scope of the claims which follow.

I claim:

1. An expansible power element comprising a rigid base member, a rigidhollow sleeve joined at one end to said base member and having the otherend open to receive a plunger, a tubular rubber element inside saidsleeve and having its side walls juxtaposed to and contained by theinside walls of said sleeve, said rubber element having one end open andthe other end closed by a transverse wall spaced from said open end,said open end of said rubber element facing the open end of said sleevefor receiving a plunger therein, said sleeve having the inside diameterreduced to form an abutment around the inside of said sleeve againstwhich the open end edge of said element engages to block movement ofsaid sidewalls of said element toward said open end of said sleeve, aplunger in said sleeve extending into the open end of said element andengaging said transverse wall, and means to apply fluid pressure to saidtransverse wall of said element on the side thereof opposite the sideengaged by said plunger for forcing said wall toward the open end ofsaid sleeve.

2. An expansible power element comprising a rigid base member, a rigidhollow sleeve joined at one end to said base member and having the otherend open to receive a plunger, a tubular rubber element open at oppositeends and disposed inside said sleeve and having its side wallsjuxtaposed to and contained by the inside walls of said sleeve, rubberwall means forming a resilient partition in said element transverselythereof, one open end of said rubber element facing the open end of saidsleeve for receiving a plunger therein, said sleeve having the insidediameter reduced to form an abutment around the inside of said sleeveagainst which the end edge of said element at said one end engages toblock movement of said sidewalls of said rubber element toward said openend of said sleeve, a plunger in said sleeve extending into said openend of said rubber element and engaging said wall means, and means toapply fluid pressure to said wall means on the side thereof opposite theside engaged by said plunger for forcing said wall means toward saidopen end of said sleeve.

3. An expansible power element comprising a rigid base member having afluid passage therein, a rigid hollow sleeve joined at one end to saidbase member and having the other end open to receive a plunger, atubular rubber member inside said sleeve and having its side wallsjuxtaposed to and contained by the inside walls of said sleeve, saidrubber member having one end open and the other end closed by atransverse wall, said open end of said rubber member facing the open endof said sleeve for receiving a plunger therein, said sleeve having theinside diameter reduced to form an abutment around the inside of saidsleeve against which the open end edge of said member engages to blockmovement of said sidewalls of said rubber member toward said open end ofsaid sleeve, a plunger in said sleeve extending into the open end ofsaid rubber member and engaging said transverse wall, a second cup-shaperubber member having the side walls thereof juxtaposed to and containedby the inside walls of said sleeve and having a transverse wall at oneend abutting the transverse wall of the first mentioned rubber member,said second cup-shape member having an open end open to said fluidpassage in said base member, means compressing peripheral portions ofthe open end of said second cup-shape member between said sleeve andbase member to form a fluidtight seal, and means to apply fluid pressurein said fluid v passage.

References Cited in the file of this patent UNITED STATES PATENTS TatterAug. 29, 1933 Durnin May 15, 1934 Erichsen Mar. 12, 1935 Vickers Apr.12, 1938 Dodge Jan. 5, 1943 ONeill Apr. 19, 1949 OTHER REFERENCESPlastics and Resins (pp. 14-16 and 36), May 1946. Modern Plastics (pp.108 and 109), November 1947.

